Epileptiform discharges evoked in hippocampal brain slices from epileptic patients

We have recorded from diseased hippocampal tissue which was surgically removed from epileptic patients for therapeutic purposes. When the perforant path was stimulated at a low frequency (1 Hz), the number of population spikes evoked in the dentate gyrus increased by a factor of as great as 8 during a 15 s train. This effect was transient. A similar epileptiform discharge could be generated in normal rat hippocampal brain slices by the same stimulus paradigm, but only in the presence of a low concentration (0.2 microM) of bicuculline. These results suggest that this frequency-dependent epileptiform discharge, evoked in the dentate gyrus of epileptic patients, may be due to a small reduction in GABAA-mediated inhibition and may involve factors that lead to the initiation of seizures.